A communication system includes a DownLink (DL) that conveys signals from transmission points such as Base Stations (BSs) or eNodeBs to User Equipments (UEs) and an UpLink (UL) that conveys signals from UEs to reception points such as eNodeBs. A UE, also commonly referred to as a terminal or a mobile station, may be fixed or mobile and may be a cellular phone, a personal computer device, and the like. An eNodeB, which is generally a fixed station, may also be referred to as an access point or other equivalent terminology.
DL signals include data signals conveying information content, control signals conveying DL Control Information (DCI), and Reference Signals (RS), which are also known as pilot signals. An eNodeB transmits data information or DCI through respective Physical DL Shared CHannels (PDSCHs) or Physical DL Control CHannels (PDCCHs). Possible DCI formats used for downlink assignment include DCI format 1A, 1B, 1C, 1D, 2, 2A, 2B, 2C and 2D. A UE can be configured with a transmission mode that determines the downlink unicast reception method for the UE. For a given transmission mode, a UE can receive unicast downlink assignment using DCI format 1A and one of DCI format 1B, 1D, 2, 2A, 2B, 2C or 2D. An eNodeB transmits one or more of multiple types of RS including a UE-Common RS (CRS), a Channel State Information RS (CSI-RS), and a DeModulation RS (DMRS). A CRS is transmitted over a DL system BandWidth (BW) and can be used by UEs to demodulate data or control signals or to perform measurements. To reduce CRS overhead, an eNodeB may transmit a CSI-RS with a smaller density in the time and/or frequency domain than a CRS. For channel measurement, Non-Zero Power CSI-RS (NZP CSI-RS) resources can be used. For Interference Measurement Resources (IMRs), CSI Interference Measurement (CSI-IM) resources associated with a Zero Power CSI-RS (ZP CSI-RS) can be used. A UE can determine the CSI-RS transmission parameters through higher layer signaling from an eNodeB. DMRS is transmitted only in the BW of a respective PDSCH and a UE can use the DMRS to demodulate information in a PDSCH.